First, make your dough. Beat 1 egg and 1/2 cup schmaltz, and then add in sifted flour, baking powder and salt and knead until you have a dough that is not sticky. If you add too much flour in, just add a little water to make your perfect dough. Cover and refrigerate for at least an hour.
Now, roast your garlic by making a packet with garlic coves and a drizzle of schmaltz or olive oil. Roast in a 400 degree oven until garlic is soft, about 40 minutes. Then lower oven to 375 degrees F.
Meanwhile, caramelize your onions by cooking in 1 Tablespoon schmaltz or olive oil and 1/2 teaspoon salt in a large saute pan over low until caramel, about 40 minutes.
Wash and peel your potatoes and cut them into even pieces. Then cover with cold water in a large saucepan and bring to a boil. Cook until you can stick a knife into the potatoes and it comes out without resistance. Then strain water, cool a little, and mix with 1/4 cup schmaltz, scallions, roasted garlic, caramelized onions, eggs, 1 teaspoon salt, and 1/2 teaspoon black pepper.
Ah beautiful schmaltz. Now let’s assemble! There are many ways to form knishes but I like individual round ones. Roll out your dough until it is as thin as you can get it. Then cut out 3 inch rounds (using a cookie cutter or wine glass works great!). Put a tablespoon of filling in each circle and scrunch up to make a knish.
Then wash with egg and bake at 375 degrees F until golden brown, about 25 minutes.
Prep time does not include time for dough to chill.